Gallery: The Smallest Alien Planets

Three Smallest Alien Planets Discovered

Credit: NASA/JPL-Caltech

This artist's concept depicts the newfound planetary system KOI-961, which contains three alien planets smaller than Earth. The exoplanets circle their red-dwaf host star at very close distances, so they're likely too hot to host life. [Full Story]

KOI-961 and Its Three Known Planets

Credit: Caltech

This artist's conception compares the KOI-961 planetary system to Jupiter and the largest four of its many moons. The KOI-961 planetary system hosts the three smallest planets known to orbit a star beyond our sun (called KOI-961.01, KOI-961.02 and KOI-961.03). Image released January 11, 2011.

Smallest Alien Planets Comparison

Credit: NASA/JPL-Caltech

This chart compares the smallest known alien planets to Mars and Earth. Astronomers using data from NASA's Kepler space telescope announced the discovery of KOI-961.01, KOI-961.02 and KOI-961.03 on Jan. 11, 2012; the Kepler team announced Kepler-20e and Kepler-20f in December 2011.[Full Story]

Former Champ: Planet Kepler-20e

Credit: NASA/JPL-Caltech/T. Pyle

An artist's rendering of the newfound alien planet Kepler-20e, which scientists say is smaller than Earth, at about 0.87 times the width of our planet.

Alien Planet Kepler-20f

Credit: NASA/JPL-Caltech/T. Pyle

This illustration shows the alien planet Kepler-20f, discovered by NASA's Kepler space telescope. At 1.03 times the width of Earth, Kepler-20f is the second smallest exoplanet yet found.

Gliese 581e: Former Small Planet Champ

Credit: ESO/L. Calcada

The former champ of most Earth-sized planets yet is a world called Gliese 581 e, which circles a star that has four planets total. It was called the smallest because of its mass, which is just 1.9 times the mass of Earth, making it the lightest known alien planet at the time.

Rocky planet Kepler-10b

Credit: NASA

Artist's concept of Kepler-10b, which was detected by NASA's Kepler mission and is about 1.4 times the radius of Earth. Kepler scientists say it's the first "unquestionably rocky" alien planet ever found. It is about 560 light-years from Earth.

Sky Map of Alien Map Kepler-21b

Credit: J. Glaspey, P. Marenfeld

The star field studied by NASA's planet-hunting Kepler space telescope, as seen over southern Arizona's Kitt Peak National Observatory. The approximate position of the alien planet Kepler-21b and its parent star HD 179070 is indicated by the circle. Kepler-21b is located 352 light-years from Earth.

Kepler-9d

Credit: NASA/Ames/JPL-Caltech

This artist's concept illustrates the two Saturn-sized planets discovered by NASA's Kepler mission around a star called Kepler-9. A 3rd planet, Kepler-9d just 1.5 times the radius of Earth, may also be orbiting the star. This is the first star system found to have multiple transiting planets.

Rocky Planet COROT-7b

This illustration depicts the hot rocky alien planet COROT-7b, a hellish world about 1.7 times the radius of Earth that orbits a star about 500 light-years away.

Kepler-11b: Almost Double Earth's Mass

Credit: Nature

This artist's illustration of the extrasolar planets discovered around the star Kepler 11 by NASA's Kepler Space Telescope. One of the planets, called Kepler-11b, is about 1.97 times the radius of Earth.

Super-Earth Exoplanet GJ 1214b

This artist’s impression shows the super-Earth exoplanet GJ 1214b passing in front of its faint red parent star. The exoplanet, orbiting a small star only 40 light-years away from us, is about 2.7 times the radius of Earth and has a mass about six times that of the Earth. GJ 1214b appears to be surrounded by an atmosphere that is either dominated by steam or blanketed by thick clouds or hazes.

Three Planets Found Around Kepler-18 Star

Credit: Tim Jones/McDonald Obs./UT-Austin

This graphic shows the orbits of the three known planets orbiting Kepler-18 as compared to Mercury's orbit around the Sun. The bottom graphic shows the relative sizes of the Kepler-18 and its known planets to the Sun and Earth. One of the planets, Kepler-18b, is about twice the size of Earth.

Diagram of super-dense alien planet 55 Cancri e transiting host star

A simulation of the silhouette of planet 55 Cancri e, which is about 2.08 times the radius of Earth but has eight times the mass, transiting its parent star, compared to the Earth and Jupiter transiting our sun, as seen from outside the solar system. The star 55 Cancri A is nearly a twin of the sun and located 40 light-years from Earth in the constellation Cancer (the Crab).

55 Cancri star system location in sky

Credit: Till Credner, AlltheSky.com

This wide-angle photograph of the night sky shows the location of 55 Cancri, a star where astronomers have found five planets, including a hot, dense super-Earth.

Alien Planet Kepler 19b

Credit: David A. Aguilar (CfA)

The "invisible" world Kepler-19c, seen in the foreground of this artist's conception, was discovered solely through its gravitational influence on the companion world Kepler-19b (the dot crossing the star's face). Kepler-19b is slightly more than twice the diameter of Earth, and is probably a "mini-Neptune." The planets orbit a star about 650 light-years away from Earth in the constellation Lyra.

Artist's Conception of Kepler-22b

Credit: NASA/Ames/JPL-Caltech

This artist's conception illustrates Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star. The planet is about 2.38 times the radius of Earth and in a star system 600 light-years from Earth.

Kepler-22 Star System Diagram

Credit: NASA/Ames/JPL-Caltech

This diagram compares our own solar system to Kepler-22, a star system containing the first "habitable zone" planet discovered by NASA's Kepler mission.

Kepler Planets Diagram

Credit: NASA/Kepler Mission/Wendy Stenzel

Comparative sizes of planets discovered by Kepler. Jupiter, Neptune and Earth are shown for comparison as well. "RE" in the diagram means size relative to Earth or RE = Radius of the planet in Earth radii.

Kepler Planets Temperatures and Sizes Chart

Credit: NASA/Ames, W. Stenzel

Chart showing temperatures and relative sizes of the Kepler planets that have been discovered.

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Three Smallest Alien Planets Discovered

Credit: NASA/JPL-Caltech

This artist's concept depicts the newfound planetary system KOI-961, which contains three alien planets smaller than Earth. The exoplanets circle their red-dwaf host star at very close distances, so they're likely too hot to host life. [Full Story]

KOI-961 and Its Three Known Planets

Credit: Caltech

This artist's conception compares the KOI-961 planetary system to Jupiter and the largest four of its many moons. The KOI-961 planetary system hosts the three smallest planets known to orbit a star beyond our sun (called KOI-961.01, KOI-961.02 and KOI-961.03). Image released January 11, 2011.

Smallest Alien Planets Comparison

Credit: NASA/JPL-Caltech

This chart compares the smallest known alien planets to Mars and Earth. Astronomers using data from NASA's Kepler space telescope announced the discovery of KOI-961.01, KOI-961.02 and KOI-961.03 on Jan. 11, 2012; the Kepler team announced Kepler-20e and Kepler-20f in December 2011.[Full Story]

Former Champ: Planet Kepler-20e

Credit: NASA/JPL-Caltech/T. Pyle

An artist's rendering of the newfound alien planet Kepler-20e, which scientists say is smaller than Earth, at about 0.87 times the width of our planet.

Alien Planet Kepler-20f

Credit: NASA/JPL-Caltech/T. Pyle

This illustration shows the alien planet Kepler-20f, discovered by NASA's Kepler space telescope. At 1.03 times the width of Earth, Kepler-20f is the second smallest exoplanet yet found.

Gliese 581e: Former Small Planet Champ

Credit: ESO/L. Calcada

The former champ of most Earth-sized planets yet is a world called Gliese 581 e, which circles a star that has four planets total. It was called the smallest because of its mass, which is just 1.9 times the mass of Earth, making it the lightest known alien planet at the time.

Rocky planet Kepler-10b

Credit: NASA

Artist's concept of Kepler-10b, which was detected by NASA's Kepler mission and is about 1.4 times the radius of Earth. Kepler scientists say it's the first "unquestionably rocky" alien planet ever found. It is about 560 light-years from Earth.

Sky Map of Alien Map Kepler-21b

Credit: J. Glaspey, P. Marenfeld

The star field studied by NASA's planet-hunting Kepler space telescope, as seen over southern Arizona's Kitt Peak National Observatory. The approximate position of the alien planet Kepler-21b and its parent star HD 179070 is indicated by the circle. Kepler-21b is located 352 light-years from Earth.

Kepler-9d

Credit: NASA/Ames/JPL-Caltech

This artist's concept illustrates the two Saturn-sized planets discovered by NASA's Kepler mission around a star called Kepler-9. A 3rd planet, Kepler-9d just 1.5 times the radius of Earth, may also be orbiting the star. This is the first star system found to have multiple transiting planets.

Rocky Planet COROT-7b

This illustration depicts the hot rocky alien planet COROT-7b, a hellish world about 1.7 times the radius of Earth that orbits a star about 500 light-years away.

Kepler-11b: Almost Double Earth's Mass

Credit: Nature

This artist's illustration of the extrasolar planets discovered around the star Kepler 11 by NASA's Kepler Space Telescope. One of the planets, called Kepler-11b, is about 1.97 times the radius of Earth.

Super-Earth Exoplanet GJ 1214b

This artist’s impression shows the super-Earth exoplanet GJ 1214b passing in front of its faint red parent star. The exoplanet, orbiting a small star only 40 light-years away from us, is about 2.7 times the radius of Earth and has a mass about six times that of the Earth. GJ 1214b appears to be surrounded by an atmosphere that is either dominated by steam or blanketed by thick clouds or hazes.

Three Planets Found Around Kepler-18 Star

Credit: Tim Jones/McDonald Obs./UT-Austin

This graphic shows the orbits of the three known planets orbiting Kepler-18 as compared to Mercury's orbit around the Sun. The bottom graphic shows the relative sizes of the Kepler-18 and its known planets to the Sun and Earth. One of the planets, Kepler-18b, is about twice the size of Earth.

Diagram of super-dense alien planet 55 Cancri e transiting host star

A simulation of the silhouette of planet 55 Cancri e, which is about 2.08 times the radius of Earth but has eight times the mass, transiting its parent star, compared to the Earth and Jupiter transiting our sun, as seen from outside the solar system. The star 55 Cancri A is nearly a twin of the sun and located 40 light-years from Earth in the constellation Cancer (the Crab).

55 Cancri star system location in sky

Credit: Till Credner, AlltheSky.com

This wide-angle photograph of the night sky shows the location of 55 Cancri, a star where astronomers have found five planets, including a hot, dense super-Earth.

Alien Planet Kepler 19b

Credit: David A. Aguilar (CfA)

The "invisible" world Kepler-19c, seen in the foreground of this artist's conception, was discovered solely through its gravitational influence on the companion world Kepler-19b (the dot crossing the star's face). Kepler-19b is slightly more than twice the diameter of Earth, and is probably a "mini-Neptune." The planets orbit a star about 650 light-years away from Earth in the constellation Lyra.

Artist's Conception of Kepler-22b

Credit: NASA/Ames/JPL-Caltech

This artist's conception illustrates Kepler-22b, a planet known to comfortably circle in the habitable zone of a sun-like star. The planet is about 2.38 times the radius of Earth and in a star system 600 light-years from Earth.

Kepler-22 Star System Diagram

Credit: NASA/Ames/JPL-Caltech

This diagram compares our own solar system to Kepler-22, a star system containing the first "habitable zone" planet discovered by NASA's Kepler mission.

Kepler Planets Diagram

Credit: NASA/Kepler Mission/Wendy Stenzel

Comparative sizes of planets discovered by Kepler. Jupiter, Neptune and Earth are shown for comparison as well. "RE" in the diagram means size relative to Earth or RE = Radius of the planet in Earth radii.

Kepler Planets Temperatures and Sizes Chart

Credit: NASA/Ames, W. Stenzel

Chart showing temperatures and relative sizes of the Kepler planets that have been discovered.